Electric Heating Element Having An Electrically Operated Heating Element And An Anode For Cathodic Corrosion Protection

ABSTRACT

The disclosure relates to an electric heating element for use in a water storage unit, comprising a metal attaching element for attaching the electric heating element on the water storage unit, an electrically operated heating element, an anode for cathodic corrosion protection, and an adjustable resistor element, wherein the heating element is electrically contacted with the attaching element and/or the water storage unit via the adjustable resistor element, and the heating element and the anode are arranged in physical proximity to one another on the attaching element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority to German Patent Application No. 10 2018 127 305.3, filed on Oct. 31, 2018. The entire disclosure of the above application is incorporated herein by reference.

FIELD

The present disclosure relates to an electric heating element having an electrically operated heating element and an anode for cathodic corrosion protection for use in a water storage unit, especially in a water storage unit for warm water.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.

In practice, such an electric heating element is used, for example, for water storage units such as storage water heaters. Storage water heaters are used to heat water for private or industrial purposes. The technical requirements for such storage water heaters are stringent. The equipment should function properly for as long a service life as possible without having a negative influence on the quality of the water. They should be resistant to corrosion and, consequently, naturally should not leak after years of operation. These requirements must be satisfied at water temperatures up to 100° C., wherein the water quality parameters, such as water hardness, electrical conductivity, and salinity, may cover a broad spectrum.

As a rule, unalloyed or low alloy steels are used as materials for constructing water storage units, and in particular storage water heaters. Therefore, in contact with water, corrosion processes on the storage water heater would unfold if oxygenated fresh water was supplied continuously. To prevent or mitigate such damages from corrosion, frequently the interior of the storage water heater is enameled. Coverage of 99.9% and more is possible when such an enamel coating is added properly. However, at least a few minor faults always occur in the enameling, so that enamel coating cannot provide 100% protection against corrosion processes. In general, therefore, enameled storage water heaters are also provided with a galvanic anode (sacrificial anode) or a stray current anode as a corrosion protection measure. As a rule, such anodes are guided through an opening in the wall of the hot water storage unit and attached to the wall. These anodes are used for cathodic corrosion protection of the steel structural material in the region of enamel faults with electrolyte contact. When the anodes are used, a protective current flows from the anode to the enamel faults (cathodes), preventing corrosion. It is possible to ensure sufficient current distribution of the protective current, the current distribution being as uniform as possible, using the structural configuration of the storage water heater and using the arrangement and number of an-odes. As a rule the anode is attached in a centered manner, that is, in the center of the normally round storage water heater to be protected, so that the potential on all surfaces of the container are approximately the same, in order to permit favorable protective current distribution across the water storage heater.

The materials of the heating element, anode, and the connector/sealing of the two elements with respect to the storage water heater are subject to multiple and very stringent requirements, due to the sometimes extremely variable water temperatures with high relative changes in temperature within the storage water heater, the varying differences in pressure due to different water levels within the storage container, and the electrochemical processes due to the cathodic corrosion protection, and the requirements for the drinking water hygiene of the water in hot water storage units are also very high.

In general, copper or copper alloys, such as brass, are used as materials for constructing the heating elements of the electric heating element. Stainless steel is also used. However, due to the use of metal-conducting heating elements, the distribution of the protective current is unfavorably influenced by the water storage unit because, as a rule, due to the construction, there is electrical contact between the anode and heating element via the wall of the water storage unit. If the anode is in physical proximity to the heating element, the anode primarily protects the heating element instead of the faulty sites in the enamel, because the heating element appears to be an external cathode. To prevent this, and to provide advantageous protective current distribution, as a rule the anode is attached far from the heating element, for example at a distance of approximately 30 to 50 cm from the heating element. It is a drawback that in general two separate openings that are spaced apart from one another must be present in the water storage unit for this. This means additional structural complexity and increases manufacturing costs.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

Proceeding from this, it is the object of the disclosure to provide an electric heating element having an anode, which electric heating element is particularly compact and makes it possible to effectively protect the water storage unit from corrosion.

Thus, according to the disclosure, an electric heating element for use in a water storage unit is provided and comprises a metal attaching element for attaching the electric heating element to the water storage unit, an electrically operated heating element, an anode of cathodic corrosion protection, and an adjustable resistor element. It is also provided that the heating element is electrically contacted with the attaching element and/or the water storage unit via the adjustable resistor element and that the heating element and the anode are arranged in physical proximity to one another on the attaching element.

It is thus an essential aspect of the disclosure that the anode and the heating element are arranged jointly and in physical proximity to one another on the attaching element. Surprisingly, the physical proximity of the anode to the heating element does not lead to lower corrosion protection. The attaching element permits the electric heating element to be attached to the water storage unit, in particular in a wall of the water storage unit. The tubes of the electric heater that extend into the interior of the storage unit are in part insulated against the attaching element via a potential adjustable resistor, the sacrificial anode is passed through the attaching element to the outside in an electrically insulated manner. Due to the physical proximity of the anode and the heating element, the extension of the attaching element is minor. Thus, due to the minor extension of the attaching element, only a small mounting opening in the water storage unit is required. According to the disclosure, it is not necessary to have a large opening, which would then have to be closed, for example, with an expensive and structurally complex flange connection. Moreover, it is also not necessary that two discrete openings be present in the wall of the water storage unit for the anode and the heating element. The extension of the attaching element is preferably between 3 and 20 cm.

Another essential aspect of the disclosure is that the heating element is connected in an electrically conducting manner to the attaching element and/or to the water storage unit via the adjustable resistor element. Not having the adjustable resistor element would lead to a short circuit between heating element and water storage unit or attaching element. The cathodic protective effect of the anode for the enameled water storage unit would be sharply reduced because of this. If the resistance in the adjustable resistor element is calculated correctly, on the other hand, the heating element is partially included in the cathodic protection of the water storage unit, so that so-called current exit corrosion is suppressed, for example, on the copper electric heating element, and on the other hand the cathodic protective potentials on the enameled container are improved, because they are more cathodic. Advantageous corrosion protection is provided, especially for water having low conductivity, due to an improved wall potential of the water storage unit. Moreover, the protective current is reduced by the construction of the electric heating element, which leads to an increase in the service life of the sacrificial anode when one of the latter is provided. The attaching element is a metal attaching element so that the corrosion protection for the water storage element is also made possible when the heating element is electrically contacted with the attaching element via the adjustable resistor element. The attaching element preferably comprises a copper alloy, such as brass. Stainless steel is also possible in principle.

An electric heating element constructed in this manner is then suitable in particular for use in water storage units, for example in a storage water heater. The cathodic protection of the water storage unit is improved and the protective current reduced by the construction of the electric heating element. The inventive electric heating element is particularly compact in terms of its construction and all that is required for mounting on the water storage unit is an opening in the wall of the water storage unit, preferably sleeve or flange.

Physical proximity of the anode to the heating element shall be construed to be a distance between the anode and the heating element that is in the range of a few millimeters to a few centimeters. In particular it shall be construed to be a distance between 1 mm to 50 mm.

An anode in the context of the present disclosure comprises any corrosion protection anodes, such as sacrificial anodes made of magnesium alloys or aluminum alloys, or stray current anodes that are used for cathodic corrosion protection of liquid-holding containers or water storage units, in particular water storage units for heated potable water.

An electrically operated heating element in the context of the present disclosure comprises any type of heating elements, such as, for example, heating rods, heating tubes, or heating coils, that are supplied electrical energy for heating the water in the water storage unit. Moreover, built-in parts are also included that are used for temperature regulation and control, such as a temperature probe.

According to one preferred refinement of the disclosure, the attaching element has a thread and may be screwed directly into the water storage unit. In this way it is possible to mount the electric heating element in a wall of the water storage unit in a simple manner. The attaching element preferably has a standardized male thread that is suitable for use in plumbing and heating equipment, such as a Whitworth pipe thread. For example, the attaching element has a cylindrical thread in the sizes G1 to G3 inches. The attaching element preferably has a cylindrical thread in the size G1 ¼ inch, which is equal to a thread diameter of approximately 41.91 mm. Both pipe threads and conical threads may be used.

According to one preferred refinement of the disclosure, the anode comprises an anode body and a contact element connected in an electrically conducting manner to the anode body, wherein the contact element is passed through the attaching element in an electrically insulated manner through an insulating pass-through. The anode body may comprise different materials depending on the type of anode (stray current or sacrificial anode). For example, the anode body for a sacrificial anode may be produced from magnesium or aluminum or, for a stray current anode, may be produced from titanium with a mixed oxide layer. In principle, the contact element be connected to the anode body in different ways. For example, it may be provided that the contact element is connected to a core running through the anode body, for example by means of welding, soldering, and/or pressing, or that the contact element is cast into the anode body.

The contact element may be embodied as a metal pin that has a thread, for example. Such an embodiment of the contact element as a metal pin is particularly simple to produce and has also proved to be very easy to manage during operation of the sacrificial anode. The contact element is passed through the attaching element in an electrically insulated manner in order to provide advantageous protective current distribution in the water storage unit. The insulating pass-through is provided for this purpose. The insulating pass-through may be realized as an injection molded part, for example, sealing preferably being accomplished using a press fit. Moreover, the insulating pass-through may be embodied as a rotational part having a male thread and a female thread. The male thread of the rotational part may be an M8 thread, for example, and the female thread may be an M4 thread.

In principle, a stray current anode or sacrificial anode may be used as the anode. When using a sacrificial anode, according to one refinement of the disclosure it is provided that the sacrificial anode for cathodic corrosion protection is connected in an electrically conducting manner to the attaching element and/or to the water storage unit. Thus an electrical contact is produced between sacrificial anode and the device to be protected. The electrical connection to the attaching element may be made, for example, via a nut. Alternatively, an electrical contact to the wall of the water storage unit may also be produced via an electrically conducting connector. This provides an opportunity to determine the electrical potential of the anode body from outside the water storage unit so that the protective current given off permits a conclusion to be drawn using a voltage measurement between the potential of the anode body, on the one hand, and the potential of the water storage unit. If this falls below a predetermined value, it must be assumed that the sacrificial anode has been “spent” and must be replaced. Moreover, there is the possibility that the consumption of the sacrificial anode may be slowed in that an ohmic resistor is switched between the contact element and the attaching element or the water storage unit. Measuring the absolute protective current between anode and container structure also permits a conclusion to be drawn about the status of the sacrificial anode, entirely in accordance with the aforesaid method for measuring voltage.

A stray current anode may be used as an alternative to using a sacrificial anode. When a stray current anode is used, according to one preferred refinement of the disclosure it is provided that the contact element for cathodic corrosion protection (titanium anode with MMO coating) is connected in an electrically conducting manner to an external voltage source. In this way stray current anodes supply protective current continuously. For regulating and controlling the protective current, stray current anodes may be equipped with a potentiostat that, on the one hand, is connected to the water storage unit and/or to the attaching element, and, on the other hand, is connected to the contact element (especially Ti anode).

The insulating pass-through is provided for the purpose of insulating the contact element of the anode from the attaching element. In principle, the insulating pass-through may be produced from any insulating polymeric material. According to one preferred refinement of the disclosure it is provided that at least parts of the insulating pass-through are produced from cross-linked polyethylene. Moreover, the insulating pass-through may also be produced exclusively from cross-linked polyethylene. The use of cross-linked polyethylene (PE-X) is associated with a number of advantages. PE-X can provide both insulation between the contact element and the water storage element, as well as sealing between the annular gap of the pass-through opening for the contact element in the attaching element. Material made of PE-X is distinguished in particular in that the material is essentially, according to generally accepted codes of practice, such as e.g. approval guidelines, hygienically safe and thus suitable for use in the field of water storage units, in particular water storage units for heated potable water.

PE-X furthermore is highly chemically resistant to bases and acids and is also highly electrochemically resistant to the effects of current. Thermal material resistance at temperatures up to 95° C., and for brief periods even up to 110° C., and long-term thermal resistance of up to approx. 20 years under the relevant operating conditions for water storage units, especially water storage units for heated potable water, is another advantageous property of PE-X. Moreover, PE-X may be produced such that there is not complete electrical insulation, but instead such that PE-X electrical conductivity is adjustable. Thus an opportunity is provided for the insulating pass-through to be used simultaneously as ohmic resistor between the contact element of the anode and the attaching element. This reduces the protective current given off by the sacrificial anode, extending the service life of the sacrificial anode.

In principle the heating element may comprise only a heating tube. According to one preferred refinement of the disclosure, however, the heating element comprises a temperature sensor, at least one heating tube, an intermediate piece, and a connecting element connected in an electrically conducting manner to the intermediate piece, wherein the connecting element passes through the attaching element through a sealing body in an electrically insulated manner. The water in the water storage unit may be heated by means of the heating tube. The temperature sensor is provided for regulating and/or controlling the temperature. The heating tube and the temperature sensor preferably comprise parts made of copper or a copper alloy, such as brass, or a nickel-based alloy. More preferably they comprise parts made of stainless steel or enameled, non-alloyed steel. The heating tube may be embodied in a U shape or may have another shape. The diameter of the heating tube is preferably between 5 and 15 mm and its length is between 200 and 500 mm; other lengths are also possible, however. The diameter of the temperature sensor is preferably between 5 and 15 mm and the length is between 150 and 350 mm.

For the purpose of mounting, the heating tube and temperature sensor are connected to the intermediate piece. The intermediate piece may be mounted on the attaching element via the connecting element. The connecting element may be a pin, a screw, or the like. It may have a male thread so that it is easy to attach. In principle the connecting element may be connected to the intermediate piece in a number of ways. One option is for the intermediate piece to have a blind bore, for example, with a thread cut into it and in which the connecting element can engage. In order to provide advantageous protective current distribution on the water storage unit, the connecting element is passed through the attaching element in an electrically insulated manner. To this end, the sealing body insulates the connecting element from the attaching element and seals the annular gap between the connecting element and the attaching element. Moreover, the sealing body may also insulate and seal the intermediate piece from the attaching element. The sealing body preferably comprises a polymer material.

According to one preferred refinement of the disclosure, the connecting element leads through the adjustable resistor element and is electrically contacted with the attaching element and/or the water storage unit via the adjustable resistor element. For improved cathodic corrosion protection, the heating element is connected in an electrically conductive manner to the attaching element and or to the water storage unit via the adjustable resistor element. This may be realized in that the connecting element is passed through the adjustable resistor element and is electrically contacted with the attaching element and/or the water storage unit via the adjustable resistor element.

In this context, according to a preferred refinement of the disclosure it is provided that the adjustable resistor element is annular, has a contact surface for electrical contacting on both an upper side and a lower side, and an ohmic resistor is interposed between the contact surfaces. Due to the annular embodiment, the connecting element may be passed through the adjustable resistor element. The electrical contact between the connecting element and the attaching element may be produced using the contact surfaces. Furthermore, according to another preferred refinement of the disclosure it is provided that the adjustable resistor element is embodied as a miniaturized plate with an SMD. This makes it possible to have reliable and production-friendly series mounting. The ohmic resistor in the adjustable resistor element is preferably between 500 and 1000 Ohms, so that the heating element is included in the cathodic corrosion protection. This inclusion of the (copper) tube elements in the cathodic protective circuit suppresses current exit corrosion thereon. Furthermore preferred, the resistance is 620 Ohms.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implantations, and are not intended to limit the scope of the present disclosure.

The disclosure is explained in the following, referencing the drawings, using a preferred exemplary embodiment.

FIG. 1 is a schematic illustration of an electric heating element according to one preferred embodiment of the disclosure;

FIG. 2 is another schematic illustration of the electric heating element from FIG. 1 according to one preferred embodiment of the disclosure;

FIG. 3 is a schematic illustration of an electric heating element according to another preferred embodiment of the disclosure; and,

FIG. 4 is a schematic illustration of an electrical heating element according to another alternative embodiment of the disclosure.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

FIGS. 1 and 2 are two schematic illustrations of a first preferred embodiment of an inventive electric heating element 10. The electric heating element 10 has an anode 12. The anode 12 has an anode body 14 made of magnesium that is electrically contacted with the contact element 16, a metal threaded pin 18 in the exemplary embodiment shown here. An insulating pass-through 22 is provided so that the metal threaded pin 18 does not have any direct contact to an attaching element 20. The electric heating element 10 may be mounted in a wall of a water storage unit with the attaching element 20. The attaching element 20 comprises brass and, for mounting purposes, has a thread 24, a male thread in the exemplary embodiment shown here, with which it may be securely screwed into a wall of the water storage unit. The insulating pass-through 22 is embodied as a rotational part, comprises cross-linked polyethylene (PE-X), and has a male thread having the size M8 and a female thread having the size M4.

A heating element (insulated via 34) is also mounted to the attaching element 20. The heating element 26 has a U-shaped heating tube 28, a temperature sensor 30, and an intermediate piece 32. The temperature sensor 30 and the heating tube 28 are connected to the intermediate piece 32, and thus attached to the attaching element 20. Like the attaching element 20, the intermediate piece 32 comprises brass. A sealing body 34 made of polymer is provided as seal and insulation between the attaching element 20 and the intermediate piece 32. The attaching element 20 has a centered inner bore (not shown) via which a connecting element 36, in this case embodied as a screw 38, can engage from the outside in a blind bore of the intermediate piece 32. When screwed in, the heating element 26 is drawn toward the sealing body 34 and sealed against the attaching element 20. The sealing body thus also acts as an insulating body. The heating element 26 is supplied energy via two electrical crimp connectors 40.

For cathodic corrosion protection, the contact element 16 of the anode 12, the metal threaded pin 18 in the simplest exemplary embodiment depicted here, is contacted with the attaching element 20 via a nut 42. Alternatively, it is also possible to produce an electrical contact to the wall of the water storage unit via an electrically conducting connector 44. In order also to include the heating element 26 in the cathodic corrosion protection, the connecting element 36, in this case the screw 38, is contacted with the attaching element 20 via an adjustable resistor element 46. The adjustable resistor element 46 is embodied as a miniaturized plate having an SMD (surface-mounted device) resistor 48. The adjustable resistor element 46 is embodied in an annular fashion so that the screw 38 can pass through the adjustable resistor element 46. On each of its upper and lower sides the plate has contact surfaces, the resistance is 620 Ohms.

FIG. 3 is a sectional depiction of another exemplary embodiment of the disclosure. Compared to the exemplary embodiment in FIGS. 1 and 2, in the exemplary embodiment shown here the sealing body 34 and the intermediate piece 32 extend across a larger region of the attaching element 20. Accordingly, the contact element 16, the metal threaded pin 18 in the exemplary embodiment illustrated here, passes through not only the attaching element 20, but also the intermediate piece 32 and the sealing body 34. The insulating pass-through 22 also insulates the metal threaded pin 18 from the intermediate piece 32 and the sealing body 34.

FIG. 4 is a sectional depiction of another alternative embodiment. In contrast to FIG. 3, however, the contact element 16 is not embodied as a threaded pin, but instead as a metal pin 50 without a thread. The intermediate piece 32 and insulating pass-through 22 are modified appropriately. In the region of the anode 12, the intermediate piece 32 has a projection 52 that is enclosed by the insulating pass-through 22. The insulating pass-through 22 is embodied as an injection molding part for this. A sealing ring 54 acts as a seal between projection 52 and insulating pass-through 22. Two sealing rings 54 are also added between the metal pin 50 and the insulating pass-through.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 

1. An electric heating element for use in a water storage unit, comprising a metal attaching element for attaching the electric heating element to the water storage unit, an electrically operated heating element, an anode for cathodic corrosion protection, and an adjustable resistor element, wherein the heating element is electrically contacted with the attaching element and/or the water storage unit via the adjustable resistor element and the heating element and the anode are arranged in physical proximity to one another on the attaching element.
 2. The electric heating element according to claim 1, wherein the attaching element has a thread and may be screwed directly into the water storage unit.
 3. The electric heating element according to claim 1, wherein the anode comprises an anode body and a contact element connected in an electrically conducting manner to the anode body, wherein the contact element is passed through the attaching element in an electrically insulated manner through an insulating pass-through.
 4. The electric heating element according to claim 3, wherein the contact element for cathodic corrosion protection is connected in an electrically conducting manner to the attaching element and/or the water storage unit.
 5. The electric heating element according to claim 3, wherein the contact element for cathodic corrosion protection is connected in an electrically conducting manner to an external voltage source.
 6. The electric heating element according to claim 3, wherein at least parts of the insulating pass-through are produced from cross-linked polyethylene.
 7. The electric heating element according to claim 1, wherein the heating element comprises a temperature sensor, at least one heating tube, an intermediate piece, and a connecting element connected in an electrically conducting manner to the intermediate piece, wherein the connecting element passes through the attaching element through a sealing/insulating body in an electrically insulated manner.
 8. The electric heating element according to claim 7, wherein the connecting element passes through the adjustable resistor element and is electrically contacted with the attaching element and/or water storage unit via the adjustable resistor element.
 9. The electric heating element according to claim 1, wherein the adjustable resistor element is annular, has a contact surface for electrical contacting on both an upper side and lower side, and an ohmic resistor is interposed between the contact surfaces.
 10. The electric heating element according to claim 1, wherein the adjustable resistor element is provided as a miniaturized plate with an SMD. 